1. Field of the Invention
The present invention relates to a surface light source device and a display device, and more particularly to a surface light source device including, as light sources, point light sources that are composed of self-luminous elements, and a display device such as a liquid crystal display device, which includes the surface light source device.
2. Description of the Related Art
A display device, for instance, a liquid crystal display device, includes a surface light source device that illuminates a back side of a transmissive liquid crystal display panel. The surface light source device includes a light guide having one side surface as an incidence surface and having one major surface as an emission surface, a light source unit that is disposed to face the incidence surface of the light guide, and a reflector that is so disposed as to surround the light source unit.
Most of light source units adopt tubular light sources, such as cold-cathode fluorescent lamps, which extend in the direction of extension of the incidence surface. In recent years, however, there is a demand for reduction in power consumption in display devices that are applied to mobile equipment such as mobile phones.
To meet the demand, there has been proposed a surface light source device that uses, as light sources, self-luminous elements such as light-emitting diodes (LED), the power consumption of which is less than that of the cold-cathode fluorescent lamp (see Jpn. Pat. Appln. KOKAI Publication No. 2003-141918 and Jpn. Pat. Appln. KOKAI Publication No. 2003-187623, for instance).
The surface light source device using the point light sources such as light-emitting diodes is encountered by the problem of how to enhance the luminance. It is difficult to dispose many point light sources toward the incidence surface of the light guide within the limited space in the vicinity of the light guide. If many point light sources are to be disposed toward the incidence surface, the outside dimensions of the peripheral region of the light guide would increase and the thickness of the light guide would increase due to enlargement of the incidence surface. This prevents reduction in size.
The luminance of the surface light source device influences the display luminance of an object to be illuminated, for example, a transmissive liquid crystal display panel. Thus, in order to realize high luminance of the object to be illuminated, it is imperative to enhance the luminance of the surface light source device.